What size hot water cylinder do I need?
Choosing the right size hot water cylinder matters. Too small and someone gets a cold shower. Too big and you pay to keep water hot that you never use. Here's how to get it right.
Start with how many people live in your home
A typical New Zealander uses about 40–60 litres of hot water a day, according to BRANZ's Level guide. Multiply that by the number of people in your home and you have a rough daily figure.
For our Energie solar thermodynamic systems, we recommend:
| Household | Cylinder | Solar panels |
|---|---|---|
| Up to 4 people | 250L | 1 |
| 5 people | 300L | 1 |
| 6 or more people | 300L | 2 |
| Large homes and high use | 500L | Ask us |
Other things that change the size you need
- Showers: long showers or high-flow shower heads use hot water fast. Cutting a 15-minute shower to 5 minutes saves around 66c each time, according to EECA.
- Baths and spa baths: a single bath can use as much as several showers.
- Guests and growing families: if you often have visitors, or the kids are becoming teenagers, go one size up.
- Mains pressure: mains pressure systems deliver more water per minute than low pressure ones, so households tend to use more.
- Space: check the height and width of your cupboard, or consider an outdoor cylinder.
Why bigger isn't always better
Every cylinder loses some heat through its walls, all day and night. The bigger the cylinder, the bigger the surface area and the more heat it loses. BRANZ recommends cylinders that are "short and broad rather than tall and slim" to reduce this loss. Choosing the size you actually need, rather than the biggest one that fits, saves you money every day.
Keeping stored water safe
Stored hot water needs to be hot enough to kill bacteria such as Legionella. EECA recommends a minimum of 60°C at the cylinder, and no more than 55°C at the tap to prevent scalding. Our systems include an automatic disinfect cycle that meets NZ Building Code clause G12. See our FAQs for details.
The size that suits a solar thermodynamic system
Because a solar thermodynamic system heats water efficiently around the clock, even at night and on cloudy days, it doesn't need an oversized cylinder to cover a shortfall. Most families of four to five need just one panel. See how it works, or compare the Eco and EcoTop systems.
Not sure what size is right for you? Contact us or call 03 540 3003 and we'll recommend the right system for your home and household. See also: how much could you save on hot water?